1. Field of the Invention
The present invention relates to a clamp of the type that rotates a clamp rod.
2. Explanation of Related Art
There is a conventional technique of the rotary clamp of this type which is constructed in the following manner, as disclosed in U.S. Pat. No. 5,820,118.
A clamp rod is inserted into a cylinder tube rotatably around an axis and axially movably. The clamp rod has a halfway height portion in an outer periphery of which there are provided oppositely inclining two helical grooves and a straight groove. An engaging ball is fitted into any one of these three grooves. The engaging ball is supported by a recess provided in a barrel portion of the cylinder tube.
The conventional technique has the following problem.
The clamp rod is supported by the cylinder tube through one engaging ball. Therefore, the clamp rod slightly inclines when it is driven for clamping and for unclamping. This reduces the accuracy of placing a clamp member provided at a leading end of the clamp rod, at a clamping position and at an unclamping position.
The present invention aims at preventing the inclination of the clamp rod.
In order to achieve the above aim, for example, as shown in FIGS. 1 to 6 or in FIGS. 7 to 10, the present invention has constructed a rotary clamp in the following manner.
A clamp rod 5 is inserted into a housing 3 rotatably around an axis and movably for clamping from one end to the other end in an axial direction. The clamp rod 5 has an outer peripheral portion formed with a plurality of guide groove 26 peripherally. The housing 3 supports a plurality of engaging members 29 which are fitted into these guide grooves 26, respectively. Each of the guide grooves 26 comprises a rotary groove 27 and a straight groove 28 provided in continuity with each other from the other end to the one end in the axial direction. The rotary grooves 27 as well as the straight grooves 28 are arranged in parallel with one another. A partition wall between the adjacent guide grooves 26, 26 has a minimum thickness (T) set to a value smaller than a groove width (W) of the guide groove 26.
The present invention offers the following advantages.
The clamp rod is provided with the guide grooves into which the engaging members are fitted, respectively. This enables the housing to peripherally and substantially evenly support the clamp rod through the engaging members. Therefore, the clamp rod can be prevented from inclining when it is driven for clamping and for unclamping. This results in improving the accuracy of placing a clamp member provided at a leading end of the clamp rod, at a clamping position and at an unclamping position.
Further, the partition wall between the adjacent guide grooves has the minimum thickness set to the value smaller than the groove width of the guide groove. Therefore, it is possible to provide many guide grooves in the clamp rod so as to support the clamp rod peripherally and substantially evenly and at the same time to decrease an inclination angle of the rotary groove. This reduces the stroke required for rotating the clamp rod to result in making the rotary clamp compact. Besides, it becomes possible to arrange a plurality of engaging members, each of which has a large diameter, adjacent one another. Therefore, a rotary mechanism of the clamp can endure a large rotation torque to result in increasing its service lifetime.
The present invention includes a clamp in which the engaging member is formed from a ball. This invention can more smoothly rotate the clamp rod and increase the service lifetime of the rotary mechanism.
Further, in order to accomplish the foregoing object, the present invention has constructed a rotary clamp in the following manner, for example, as shown in FIGS. 1 to 6.
A clamp rod 5 is inserted into a housing 3 rotatably around an axis and movably for clamping from one end to the other end in an axial direction. The clamp rod 5 has an outer peripheral portion formed with a plurality of guide grooves 26 peripherally. The housing 3 supports a plurality of engaging balls 29 which are fitted into the guide grooves 26, respectively. Each of the guide grooves 26 comprises a rotary groove 27 and a straight groove 28 provided in continuity with each other from the other end to the one end in the axial direction. The rotary grooves 27 as well as the straight grooves 28 are arranged in parallel with one another. A partition wall between the adjacent guide grooves 26, 26 has a minimum thickness (T) set to a value smaller than a diameter (D) of the engaging ball 29.
This invention also offers the same advantages as those of the above-mentioned invention.
The clamp rod can be prevented from inclining when it is driven for clamping and for unclamping. This results in improving the accuracy of placing a clamp member provided at a leading end of the clamp rod, at a clamping position and at an unclamping position. In addition, it is possible to reduce the stroke required for rotating the clamp rod, which leads to the possibility of making the rotary clamp compact. Besides, it becomes possible to arrange a plurality of engaging balls, each of which has a large diameter, adjacent one another. Therefore, a rotary mechanism of the clamp can endure a large rotation torque to result in increasing its service lifetime.
The present invention, for example, as shown in FIGS. 1 to 4 or in FIGS. 7 to 10, includes the following clamp.
The engaging balls 29 are rotatably supported by through holes 31 provided in the housing 3 and a sleeve 35 is rotatably and externally fitted over the engaging balls 29. This invention offers the following advantage.
When the clamp rod rotates, almost only rolling friction acts between an inner peripheral surface of the sleeve and the engaging balls, but sliding friction hardly acts therebetween. This reduces a resistance which acts from the sleeve to the engaging balls to result in decreasing a frictional force which acts from the engaging balls to the rotary grooves and therefore smoothly rotating the clamp rod with a light force.
The present invention also includes a clamp which is provided with at least three guide grooves. This invention is preferable due to the fact that it supports the clamp rod peripherally and substantially evenly and decreases the inclination angle of the rotary groove.
The present invention further includes a clamp which has the guide grooves arranged peripherally of the clamp rod at substantially the same spacing. This invention is preferable for supporting the clamp rod more evenly.
Moreover, the present invention, for instance, as shown in FIG. 4, FIG. 5 or FIG. 6, includes the following clamp.
The clamp rod 5 has the other end potion provided with the above-mentioned guide grooves 26. Each of the guide grooves 26 includes the rotary groove 27 provided at its other end portion with a stopper wall 45 which receives the engaging member or ball 29. The stopper wall 45 has a receiving surface 45a which fits with the engaging member or ball 29. This invention offers the following advantage. When the clamp rod rotates and retreats, the receiving surface of the stopper wall fits with the engaging member or ball to inhibit the clamp rod from rotating. This results in stopping the rotation of the clamp rod with a high accuracy.
Besides, the present invention, for example, as shown in FIG. 1, includes the following clamp. An annular piston 15 is inserted into the housing 3 axially movably. The clamp rod 5 is inserted into the piston 15. A radial bearing 24 is arranged between the piston 15 and the clamp rod 5. This invention offers another advantage of more smoothly rotating the clamp rod.